This invention relates generally to key switches, and more particularly, to contactless key switches.
One of the problems associated with key switches employing contacts is that the contacts tend to become dirty or oxidized and result in an erratic operation of the key switch. Consequently, contactless key switches have been developed in an effort to eliminate these problems. Two such contactless key switches are described in U.S. Pat. Nos. 2,881,402 and 3,719,902.
While the prior art key switches do eliminate most of the problems caused by erratic contact operation, the prior art key switches are rather complex. For example, the structures described in the two referenced patents utilize a transformer having primary and secondary windings and apparatus for altering the coupling between the windings when the key switch is depressed. The structure of the U.S. Pat. No. 2,881,402 employs apparatus for altering the relative position of the two windings to alter the coupling, and the U.S. Pat. No. 3,719,902 utilizes a shorted turn to reduce the Q of one of the windings. In both structures, a coil spring is used to bias the key switch in the undepressed position under normal conditions.